This invention relates to a method of inhibiting corrosion of zirconium or its alloy, particularly zirconium or its alloy used as material for a chemical device, a nuclear reactor or the like.
It has been reported that even zirconium or its alloy having excellent corrosion resistance under various circumstances is corroded to cause pitting or the like under severe corroding conditions as chemical processes, since it is affected by a combination of temperature, pressure, pH, reagents and by-products. Under these circumstances, it has eagerly been demanded to further improve the corrosion resistance of metals such as zirconium or its alloy in the field of the chemical industry in which highly corrosive environments are realized.
To improve the corrosion resistance of zirconium or its alloy used as a material for a chemical device, there has been proposed a process wherein it is treated with only nitric acid or with a mixture of nitric acid and another acid. (Japanese Laid-Open Patent No. 39785/83).
The above conventional method of corrosion inhibition have the defects that a protective film cannot be formed easily on the surface of zirconium or its alloy and that no sufficient corrosion resistance can be obtained.
Also the surfaces of nuclear reactor members made of zirconium or its alloy are washed with an acid solution and then autoclaved for use. (Japanese Laid-Open Patent No. 31118/80).
However, in the autoclaving, the product is kept at a temperature of as high as 400.degree. C. under a pressure of as high as 105 kg/cm.sup.2 for a long time and many steps are required for the treatment. In addition, when the acid used for the pretreatment remains on the product, the corrosion resistance of the product is deteriorated seriously due to the remaining acid.